package com.litongjava.utils.base64;

import java.io.ByteArrayOutputStream;

public class Base64Utils {
  private static final char[] base64EncodeChars = new char[] { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K',
      'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h',
      'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4',
      '5', '6', '7', '8', '9', '+', '/' };

  private static byte[] base64DecodeChars = new byte[] { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62,
      -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
      10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31,
      32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1 };

  /**
   * 编码
   */
  public static String encode(byte[] data) {
    StringBuffer sb = new StringBuffer();
    int len = data.length;
    int i = 0;
    int b1, b2, b3;

    while (i < len) {
      b1 = data[i++] & 0xff;
      if (i == len) {
        sb.append(base64EncodeChars[b1 >>> 2]);
        sb.append(base64EncodeChars[(b1 & 0x3) << 4]);
        sb.append("==");
        break;
      }
      b2 = data[i++] & 0xff;
      if (i == len) {
        sb.append(base64EncodeChars[b1 >>> 2]);
        sb.append(base64EncodeChars[((b1 & 0x03) << 4) | ((b2 & 0xf0) >>> 4)]);
        sb.append(base64EncodeChars[(b2 & 0x0f) << 2]);
        sb.append("=");
        break;
      }
      b3 = data[i++] & 0xff;
      sb.append(base64EncodeChars[b1 >>> 2]);
      sb.append(base64EncodeChars[((b1 & 0x03) << 4) | ((b2 & 0xf0) >>> 4)]);
      sb.append(base64EncodeChars[((b2 & 0x0f) << 2) | ((b3 & 0xc0) >>> 6)]);
      sb.append(base64EncodeChars[b3 & 0x3f]);
    }
    return sb.toString();
  }

  /**
   * 解码
   */
  public static byte[] decode(String str) throws Exception {
    byte[] data = str.getBytes("GBK");
    int len = data.length;
    ByteArrayOutputStream buf = new ByteArrayOutputStream(len);
    int i = 0;
    int b1, b2, b3, b4;

    while (i < len) {

      /* b1 */
      do {
        b1 = base64DecodeChars[data[i++]];
      } while (i < len && b1 == -1);
      if (b1 == -1) {
        break;
      }

      /* b2 */
      do {
        b2 = base64DecodeChars[data[i++]];
      } while (i < len && b2 == -1);
      if (b2 == -1) {
        break;
      }
      buf.write((b1 << 2) | ((b2 & 0x30) >>> 4));

      /* b3 */
      do {
        b3 = data[i++];
        if (b3 == 61) {
          return buf.toByteArray();
        }
        b3 = base64DecodeChars[b3];
      } while (i < len && b3 == -1);
      if (b3 == -1) {
        break;
      }
      buf.write(((b2 & 0x0f) << 4) | ((b3 & 0x3c) >>> 2));

      /* b4 */
      do {
        b4 = data[i++];
        if (b4 == 61) {
          return buf.toByteArray();
        }
        b4 = base64DecodeChars[b4];
      } while (i < len && b4 == -1);
      if (b4 == -1) {
        break;
      }
      buf.write(((b3 & 0x03) << 6) | b4);
    }
    return buf.toByteArray();
  }
}